Generally, in the blast furnace method which forms the main trend of the current molten iron manufacturing process, the raw material has to have a certain strength and has to have a particle size to ensure gas permeability. Further, coke is used as the carbon source for providing a fuel and a reducing agent. As the raw iron ore, sintered agglomerates are used. Accordingly, the currently used blast furnace has a coke manufacturing facility and an iron ore sintering facility as the auxiliary facilities. The auxiliary facilities require an enormous expenditure, and bring environmental problems. The environmental problems require an investment in anti-pollution facilities, with the result that the investments in the facilities are increased. Therefore, the competitiveness of the blast furnace is speedily faded.
In efforts for coping with this situation, research and development are being carried out to replace the coke with general coal, and to replace the iron ore agglomerates with direct fine iron ore which occupies more than 80% of the total world production.
A molten iron manufacturing facility which directly uses general coal and fine iron ore is disclosed in Austrian Patent Application No. AT2096/92.
This facility includes 3-stage fluidized bed type furnaces including a pre-heating furnace, pre-reducing furnaces and a final reducing furnace, and a melter-gasifier having a coal packed bed within it. In the manufacturing method using this molten iron manufacturing facility, a normal temperature fine iron ore is continuously charged into an uppermost reaction chamber (a pre-heater) to pass through the 3-stage fluidized bed type furnaces so as to be contacted with a high temperature reducing gas supplied from the melter-gasifier. During this process, the temperature of the fine iron ore is raised and its reduction is realized by more than 90%. The reduced fine iron ore is continuously charged into the melter-gasifier in which the coal packed bed is formed so as to be melted within the coal packed bed. Thus a molten iron is manufactured and discharged to the outside.
Meanwhile, a general lump coal is continuously charged into the top of the melter-gasifier to form a coal packed bed of a certain height. Further, oxygen is injected through a plurality of tuyere holes which are formed on a lower portion of the outer wall of the melter-gasifier. Thus the coal of the coal packed bed is burned and the combustion gas rises to form a stream of a high temperature reducing gas so as to be supplied to the three pre-reducing furnaces.
Meanwhile, within the melter-gasifier, the high temperature gas stream has a high velocity and, therefore, a large amount of fine dusts of the fine iron ore is inclined to be elutriated or carried out of the furnaces. In order to prevent this phenomenon, a large space is provided above the coal packed bed. In this manner, the elutriation of the fine dusts is maximally inhibited. However, the average flow velocity within the mentioned space is about 0.5 m/sec. Therefore, it is inevitable that the high temperature fine iron ore having a size of 100 .mu.m or less and the coal dusts of 400 .mu.m or less are elutriated to the outside of the furnace. Particularly, considering the particle size distribution of the high temperature fine iron ore, the particles of 100 .mu.m or less occupy 30-35 wt. %. Thus, a large amount of the reduced fine iron ore is elutriated out of the furnace. Accordingly, a high iron loss is caused and, therefore, the yield and productivity of this molten iron manufacturing process are greatly lowered.